CoLtzE— On Hemitrypa hibernica. 137 
derberg) strata. The last-named is figured in the “ Paleeontology 
of the State of New York,” vol. vi., pl. xxii., figs. 13-18; but the 
transverse section given is probably too small to convey a correct 
impression. Ulrich, however (9, pp. 559-565, and pls. xliv. 
and lvii.), has discussed six additional species, one of which is 
Devonian, while the remainder are from the Lower Carboniferous 
series. His sections (ébéd., pl. lvii.) are admirably illustrative. 
He reintroduces Prout’s Fenestella hemitrypa under the name of 
Hemitrypa proutana; and the resemblances are undoubtedly close. 
If the type-specimen really has such small openings in the sheath 
as figured by Prout, the wearing away of the surface, as already 
hinted, would give the more open mesh figured and described by 
Ulrich (9, pl. Ivii., fig. 1). Ulrich describes the fenestrules in 
his specimen as quadrangular on the reverse, and long oval on the 
obverse. Prout believed his to be slit-like or even closed on the 
reverse (8, p. 445); but the two species may at present be regarded 
as identical. HH. proutana acquires an interest in this country as 
being a decidedly near relative of the Ivish A. hibernica. 
The specimens collected by Mr. Kirwan made it necessary to 
seek the type-specimen of M‘Coy’s species, which was known to 
have formerly been in the collection of Sir R. Griffith, now in 
the Museum of Science and Art, Kildare-street, Dublin. Dr. V. 
Ball, F.R.S., has kindly allowed me to examine the collection, 
_ and specimens have been selected that exhibit well the characters 
figured by M‘Coy. The one to which I attach especial weight 
resembles his figure (2, pl. xxix, fig. 7) sufficiently closely to have 
been the type, if we may suppose that some irregularities were 
omitted in the drawing and that the lower portion has been since 
removed. No other specimen agrees approximately with the figure. 
In any case, there is sufficient agreement among the more perfect 
Trish specimens to enable us to redefine Hemitrypa hibernica. 
In so doing, I have greatly felt the need of a term for the 
“outer sheath,” and one that could also be used adjectivally. I 
venture here to employ ¢egmen for this purpose. It may be worth 
remarking that Ulrich very properly speaks of the openings in the 
tegminal mesh as “interstices,” while M‘Coy and others have used 
the term “interstice ”’ for the main columns, branches, or ribs, of 
Fenestellida. In the following description I follow M‘Coy’s 
original mode of definition as far as possible. 
